Sorting, Reversing, and Searching in Arrays in C#

This article has been excerpted from book "The Complete Visual C# Programmer's Guide from the Authors of C# Corner".

You can search for the occurrence of a value in an array with the IndexOf and LastIndexOf member functions. IndexOf starts the search from a lower subscript and moves forward, and LastIndexOf starts the search from an upper subscript and moves backwards. Both functions achieve a linear search, visiting each element sequentially until they find the match forward or backward.

Listing 20.13 illustrates a linear search through an array using the IndexOf and LastIndexOf methods.

Listing 20.13: Array Linear Search

// Linear Search
using System;

public class LinearSearcher
{
    public static void Main()
    {
        String[] myArray = new String[7] { "kama", "dama", "lama", "yama", "pama", "rama", "lama" };
        String myString = "lama";
        Int32 myIndex;

        // Search for the first occurrence of the duplicated value in a section of the
        myIndex = Array.IndexOf(myArray, myString, 0, 6);
        Console.WriteLine("The first occurrence of \"{0}\" between index 0 and index 6 is at index {1}.", myString, myIndex);

        // Search for the last occurrence of the duplicated value in a section of the
       myIndex = Array.LastIndexOf(myArray, myString, 6, 7);
        Console.WriteLine("The last occurrence of \"{0}\" between index 0 and index 6 is at index {1}.", myString, myIndex);
        Console.ReadLine();
    }
}

The program in Listing 20.13, has this output:



The String class provides methods for sorting, searching, and reversing that are easy to use. Note that Sort, BinarySearch, and Reverse are all static functions and are used for single-dimensional arrays.

Listing 20.14 illustrates usage of the Sort, BinarySearch, and Reverse functions.

Listing 20.14: Array Sort, Binarysearch, and Reverse Examples

// Binary Search
// Note an EXCEPTION occurs if the search element is not in the list
// We leave adding this functionality as homework!

using System;

class linSearch
{
    public static void Main()
    {
        int[] a = new int[3];
        Console.WriteLine("Enter number of elements you want to hold in the array (max3)?");
        string s = Console.ReadLine();
        int x = Int32.Parse(s);
        Console.WriteLine("--------------------------------------------------");
        Console.WriteLine("\n Enter array elements \n");
        Console.WriteLine("--------------------------------------------------");

        for (int i = 0; i < x; i++)
        {
            string s1 = Console.ReadLine();
            a[i] = Int32.Parse(s1);
        }

        Console.WriteLine("Enter Search element\n");
        Console.WriteLine("--------------------------------------------------");
        string s3 = Console.ReadLine();
        int x2 = Int32.Parse(s3);

        // Sort the values of the Array.
        Array.Sort(a);

        for (int i = 0; i < x; i++)
        {
            Console.WriteLine("--------------Sorted-------------------------");
            Console.WriteLine("Element{0} is {1}", i + 1, a[i]);
        }

        // BinarySearch the values of the Array.
        int x3 = Array.BinarySearch(a, (Object)x2);
        Console.WriteLine("--------------------------------------------------");
        Console.WriteLine("BinarySearch: " + x3);
        Console.WriteLine("Element{0} is {1}", x3, a[x3]);
        Console.WriteLine("--------------------------------------------------");

        // Reverse the values of the Array.
        Array.Reverse(a);
        Console.WriteLine("-----------Reversed-------------------------------");

        for (int i = 0; i < x; i++)
        {
            Console.WriteLine("----------------------------------------------");
            Console.WriteLine("Element{0} is {1}", i + 1, a[i]);
        }
    }
}

Listing 20.15 is a more sophisticated example of using the IComparer interface and Sort function together. The IComparer interface allows you to define a Compare method in order to do a comparison between two elements of your array. This Compare method is called repeatedly by the Sort function in order to sort the array. Listing 20.15 defines a Compare method that does a comparison between two strings.

Listing 20.15: Array Sorting

// sort an array according to the Nth element
using System;
using System.Collections;

public class CompareX : IComparer
{
    int compareFrom = 0;
    public CompareX(int i)
    {
        compareFrom = i;
    }

    public int Compare(object a, object b)
    {
        return String.Compare(a.ToString().Substring(compareFrom),
        b.ToString().Substring(compareFrom));
    }
}

public class ArrListEx
{
    ArrayList arr = new ArrayList();
    public ArrListEx()
    {
        arr.Add("aaaa9999");
        arr.Add("bbbb8888");
        arr.Add("cccc7777");
        arr.Add("dddd6666");
        arr.Sort(new CompareX(4));
        IEnumerator arrList = arr.GetEnumerator();

        while (arrList.MoveNext())
        {
            Console.WriteLine("Item: {0}", arrList.Current);
        }
    }

    public static void Main(string[] args)
    {
        new ArrListEx();
    }
}

Conclusion

Hope this article would have helped you in understanding Sorting, Reversing, and Searching in Arrays in C#. See other articles on the website on .NET and C#.

The Complete Visual C# Programmer's Guide covers most of the major components that make up C# and the .net environment. The book is geared toward the intermediate programmer, but contains enough material to satisfy the advanced developer.